The use of stripping layers in various photographic products is well known. Such layers have been employed, for example, in stripping films for transferring an image-bearing layer or layers from one support to another and in diffusion transfer photographic processes to facilitate separation of the image-receiving layer carrying the final transfer image from the photosensitive layer(s). Materials previously disclosed as useful for stripping layers include gum arabic; cellulose derivatives, e.g., hydroxyethyl cellulose, carboxymethyl cellulose, ethyl cellulose and cellulose acetate hydrogen phthalate; polyethylene glycol; sodium alginate; polyvinyl alcohol; polyvinyl pyrrolidone; polymethacrylic acid; and ethylene/maleic anhydride-acid copolymers.
A number of diffusion transfer processes for forming images in both silver and in dye have been disclosed in the art and need not be described in detail. In processes of this type, an exposed silver halide layer is treated with a processing composition whereby the exposed silver halide is developed and an imagewise distribution of diffusible image-forming components is formed in the unexposed and undeveloped portions of the silver halide layer. This distribution of image-forming components is transferred by imbibition to an image-receiving layer in superposed relationship with the silver halide layer to provide the desired transfer image. In color diffusion transfer processes, image formation relies upon a differential in mobility or solubility of image dye-providing material obtained as a function of development so as to provide an imagewise distribution of such material which is more diffusible and which, therefore, may be selectively transferred to an image-receiving layer comprising a dyeable stratum. This differential in mobility or solubility may be obtained, for example, by a chemical action such as a redox reaction, a siliver ion-assisted cleavage reaction or a coupling reaction.
In any of these color systems, multicolor images may be obtained by employing a photosensitive element containing at least two selectively sensitized silver halide layers each having associated therewith an image dye-providing material exhibiting the desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-, a green- and a red-sensitive siliver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan image dye-providing material.
The photosensitive element and the image-receiving element may be separate components which are brought together during processing, or they may together comprise a unitary structure, e.g., an integral negative-positive film structure wherein the photosensitive element and image-receiving element are laminated and/or otherwise physically retained together at least prior to image formation. The resulting image may be revealed by separation of the image-receiving element from the photosensitive element subsequent to processing, although processes employing integral negative-positive film units are now well known in the art wherein the image-receiving component containing the dye transfer image need not be separated from the photosensitive element for viewing purposes.
The prior art contains several references to diffusion transfer film units which include a stripping layer to facilitate removal of the image-receiving component from the remainder of the film unit. U.S. Pat. No. 2,759,825 discloses the use of stripping layers comprising a hydrophilic colloid, e.g., cellulose derivatives, in silver diffusion transfer processes, and U.S. Pat. No. 4,009,031 discloses the use of stripping layers comprising a hydrophilic colloid and ammonia in color diffusion transfer processes employing polyvinylpyridine as the dyeable stratum, i.e., the image-receiving layer. As disclosed in these patents, the stripping layer is coated over the image-receiving layer and facilitates separation of the image-receiving component comprising the overcoated image-receiving layer from the layer of processing composition applied between the photosensitive and image-receiving elements. U.S. Pat. Nos. 2,983,606, 3,227,550 and 3,658,524 disclose color diffusion transfer film units wherein the photosensitive layer(s) and dyeable stratum are located in the same rather than in separate elements. As disclosed in the latter patents, a stripping layer is disposed between the photosensitive layer(s) and their associated image dye-providing material and an underlying dyeable stratum comprising the image-receiving layer. The processing composition is applied to the surface of the photosensitive layer(s) opposite the image-receiving layer, and subsequent to processing, the stripping layer aids in the separation of the dyeable stratum from the photosensitive layer(s) to reveal the final transfer image.
The present invention is concerned with novel stripping layers which are particularly useful in photographic products of the latter type where the stripping layer is disposed between a dyeable stratum and a photosensitive component, which dyeable stratum is separated from said photosensitive component subsequent to processing and transfer image formation.